Piston for an internal combustion engine

ABSTRACT

The invention relates to a piston for an internal combustion engine comprising piston-pin bores, into which lubrication grooves that run around the nadir and equator zones of said bores are machined. The aim of the invention, is to simplify the production of the piston-pin bores provided with said lubrication grooves. To achieve this, each of the lubrication grooves has a central region, whose groove base has a depth of less than 100 μm. Said central region is flanked by groove areas facing towards the interior and exterior of the piston. The bases of said grooves are inclined towards the longitudinal axis, each forming an acute angle with the longitudinal axis of the piston-pin bore.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of German Application No.102 55 731.4 filed Nov. 29, 2002. Applicant also claims priority under35 U.S.C. §365 of PCT/DE2003/003928 filed Nov. 27, 2003. Theinternational application under PCT article 21(2) was not published inEnglish.

The invention relates to a piston for an internal combustion engine, inaccordance with the preamble of claim 1.

It is known, from the Offenlegungsschrift DE 38 30 033 A1, to machine alubrication groove into the pin bore of a piston for an internalcombustion engine, which groove runs over the nadir and the equatorregion of said bore, thereby causing an oil reservoir that serves forlubrication of the piston pin that is introduced into the pin bore.Usually, in this connection, at first the pin bore is lathed into thepin boss by means of a preliminary lathe tool, after which the insidesurface of the pin bore is precision-machined, within the scope of asecond method step. The actual lubrication groove is milled into thefinished pin bore only in a third method step.

Proceeding from this, the invention is based on the task of structuringthe pin bore of a piston for an internal combustion engine, which hasbeen provided with a lubrication groove, in such a manner that itsproduction can be simplified and made less expensive.

The solution for this task is indicated in the characterizing part ofthe main claim.

Practical embodiments of the invention are the subject of the dependentclaims.

The configuration of the lubrication groove of a pin bore, according tothe invention, has the advantage, in this connection, that after the pinbore is lathed, only a single further method step is required forprecision-machining of the pin bore and for producing the lubricationgroove, since parallel to the precision-machining of the pin bore, onlyrelative movements between the piston and the lathe tool, correspondingto the shape of the lubrication groove, are required, in order to lathethe lubrication groove, which is configured as a flat groove, into theinside surface of the pin bore.

An exemplary embodiment of the invention is explained below, using thedrawings. These show:

FIG. 1 a piston in section, with pin bores that each have a lubricationgroove according to the invention,

FIG. 2 an enlargement of the detail II from FIG. 1, with a sectionalrepresentation of the lubrication groove, and

FIG. 3 a partial section through the piston along the line III—III inFIG. 1, with a side view of the lubrication groove.

FIG. 1 shows a piston 1 for an internal combustion engine, in section,with a piston head 2 onto which two pin bosses 3 and 4, each having apin bore 5 and 6, are formed. In the section direction chosen in FIG. 1,one of the two skirts 7 of the piston 1 is shown in a top view.

A lubrication groove 8, 9, is worked into the center region of the pinbores 5, 6, in each instance, which, as shown in FIG. 2, an enlargeddetail II of FIG. 1, has a center region 10 whose groove root 11 liesparallel to the longitudinal axis 12 of the pin bores 5. Towards theinside of the piston, the region 10 is followed by a groove region 13,the groove root 14 of which is inclined at a slant towards the inside ofthe piston and in the direction of the longitudinal axis 12, andencloses an acute angle α of less than 10°, preferably less than 3°,with a longitudinal direction of the pin bore 5. Towards the outside ofthe piston, the center region 10 is followed by a groove region 15, thegroove root 16 of which is inclined at a slant towards the outside ofthe piston and also in the direction of the longitudinal axis 12, andencloses the same angle α of less than 10°, preferably less than 3°,with the longitudinal direction of the pin bore 5. The lubricationgroove 9 in the pin bore 6 has the same shape as the lubrication groove8. The depth x of the center regions 10 of the two lubrication grooves 8and 9 has a value of approximately 40 to 60 μm.

In FIG. 1 it is indicated, and in FIG. 3, a side view of the lubricationgroove 8 that is not to scale, a partial section along the line III—IIIin FIG. 1, it is clearly evident that the lubrication groove 8 (justlike the lubrication groove 9) is machined into the nadir region and theequator region of the pin bore 5, and covers a region of approximately270°. In this connection, a region of approximately 90° thereforeremains free of grooves at the zenith, resulting in the advantage thatthe surface pressure of the zenith region, which results under theeffect of the force of the work cycle when the piston pin is introduced,is not impaired by a lubrication groove.

The lubrication grooves 8 and 9 each form an oil reservoir that assuresthe oil supply for lubrication of a piston pin introduced into the pinbore 5, 6, not shown in the figures, both during start-up of an engineequipped with the piston 1, and during continuous operation of theengine. This oil reservoir is filled by means of the pump effect of thepiston pin that deforms during engine operation, so that a separate oilfeed is not necessary for this purpose.

The lubrication grooves 8 and 9 are produced in the same manner asconventional shaped bores machined into the ends of pin bores. In thisconnection, the actual pin bores 5, 6 are first lathed into the pinbosses 3, 4 by means of a preliminary lathe tool. Subsequently, theinside surfaces of the pin bores 5, 6 are precision-machined by means ofa lathe tool having a blade that projects laterally and, at the sametime, the lubrication grooves 8, 9, which are configured as flatgrooves, are lathed into the inside surfaces of the pin bores 5, 6.

Since the lubrication grooves 8, 9 cover only approximately 270° of thenadir and equator regions of the inside surfaces of the pin bores 5, 6and have the sickle shape shown in FIG. 3, in section, during theproduction of the lubrication grooves 8, 9 the lathe tool, which is putinto rotation, must be deflected so far, in the region of thelubrication grooves 8, 9, during each individual rotation, that therequired depth of the lubrication grooves 8, 9, at 40 to 60 μm, isachieved.

Alternatively to this, when the lathe tool is put into rotation, thepiston 1 can always be deflected a little bit whenever the blade of thelathe tool is located in that region of the inside surface of the pinbore 5, 6 into which the lubrication groove 8, 9 is to be lathed.

It is advantageous, in this connection, that after the pin bores havebeen lathed, only a single further method step is required for producingthe lubrication grooves 8, 9 according to the invention, since parallelto the precision machining of the inside bore surfaces, only relativemovements between the piston and the lathe tool, corresponding to theshape of the lubrication grooves 8, 9, are necessary to produce thelubrication grooves 8, 9.

REFERENCE SYMBOLS

-   1 piston-   2 piston head-   3 pin boss-   4 pin boss-   5 pin bore-   6 pin bore-   7 skirt-   8 lubrication groove-   9 lubrication groove-   10, 10′ center region-   11 groove root of the center region 10-   12 longitudinal axis-   13, 13′ groove region-   14 groove root of the region 13-   15, 15′ groove region-   16 groove root of the region 15

1. A piston for an internal combustion engine, comprising: a piston head; two pin bosses formed onto the piston head; at least one semi-circular lubricating groove machined into center regions of inside surfaces of the pin bores when viewed in a direction of a longitudinal axis of the pin bores, said at least one groove being circumferential at least over a nadir region and an equator region of the pin bores, said at least one groove having a center region with a flat cross section and a transverse width that lies parallel to the longitudinal axis of the pin bore and has a depth of less than 100 μm as compared with the inside surface of the pin bore, wherein toward an inside of the piston, the center region of the at least one lubrication groove is followed by a groove region which is inclined at a slant towards the inside of the piston and in the direction of the longitudinal axis, and encloses an acute angle of less than 3° with the longitudinal direction of the pin bore, and wherein towards an outside of the piston, the center region of the at least one lubrication groove is followed by a groove region that is inclined at a slant towards the outside of the piston and also in the direction of the longitudinal axis, and encloses an acute angle of less than 3° with the longitudinal direction of the pin bore.
 2. A piston according to claim 1, wherein the depth of the groove in the center region of the at least one lubrication groove is 40 to 60 μm relative to the inside surface of the pin bore.
 3. A piston according to claim 1, wherein more than one lubrication groove is machined into each of the pin bores. 